On Mon, 2006-09-18 at 11:11 +0200, Harald Armin Massa wrote:
> Gevik,
> >uniqueness is never a guaranteed. that is according to the RFC docs.
> 
> >uniqueness is never a guaranteed in the sense that there is a tiny
> >chance someone of the other side of the planet might generate the
> same 
> >guid. 
> 
> As much as I learned, it is recommended to give information about
> "grade of uniqueness". I think it would be a valuable information,
> which information your UUID-generator takes into account, and what the
> "grade of uniqueness" is. 
> 
> (I know of the Windows UUID, which takes the MAC-Address of the
> included Ethernet-Card into it's calculation, which may be guaranteed
> to be unique)
> 

> 
> Some more questions about UUIDs and your patch:
> 
> a) compatibility of UUIDs   -> I have generated a lot of UUIDs via the
> WIN32 provided function (for the unix-only-people: Windows uses UUIDs
> all around its registry, software IDs and on and on). How unique are
> those UUIDs when mixed with "your" UUIDs ? 


The new_guid() generates a random guid in the range of 256^256 which is 
3.231700607131100730071487668867e+616 (easy to imagine) using PG's
randomizer. I wonder how often someone could actually generate a
duplicate guid in this range. This also goes for the MS version of the
guid. It uses the MAC address and a timespamp but what happens if by
chance your PC's clock is set in the past!

> 
> b) I read some time ago about the problems with UUIDs as primary keys
> in contrast to serials: serials get produced in ascending order; and
> often data which was produced in one timespan is also connected
> semantically. "near serial values" are also local within a
> btree-index; but UUIDs generated in "near times" are usually spread
> around the possible bitranges. 
> (example for sequence of serials: 1 - 2 - 3 - 4 - 5 - 6
>  example for sequence of UUIDs : 1 - 999919281921843191 - 782 -
> 18291831912318971231)
> that is supposed to affect the locality of the index, and from that
> also the performance of the system. 
> 
> I do not know how valid this information is; so I am asking you for
> your feedback; especially since you put a lot of thoughts into this
> UUID patch. Maybe you took allready care of this situation when
> constructing the index operators? 

I am running many test regarding indexing of the uuid datatype with
large amount of records. But the performance test is still limited to
hardware capacity 

Thank you.
> 
> Thanks
> 
> Harald
> 
> 
> 
> 
> 
> 
> -- 
> GHUM Harald Massa
> persuadere et programmare
> Harald Armin Massa
> Reinsburgstra├če 202b
> 70197 Stuttgart
> 0173/9409607
> -
> Let's set so double the killer delete select all.


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